1. Field of the Invention
The present invention relates to an onboard (mounted in a vehicle) navigation system.
2. Description of Background Information
Recently, navigation systems to be mounted in a vehicle have been developed and are entering into a stage of practical application. Those navigation systems are constructed such that digitized map data is previously stored in a memory, map data of a region covering a given area including the present position of the vehicle is read out from the memory while the present position of the vehicle is being recognized, so that a map around the position of the vehicle is displayed on a display, and a "vehicle's position" indicating the present position of the vehicle is automatically indicated in the map being displayed.
In the case of such navigation systems, there are two methods for displaying a positional relationship between the map and the vehicle in which the navigation system is mounted. The first method is such that a map is displayed in a fixed positional relationship relative to the display and the display position of the vehicle is moved relative to the map. Another method is that the display position of the vehicle is fixed at the center of the display and the map is displayed in a scrolling manner. Since the map of a region having a given area around the vehicle's position is displayed, the latter method can always display the map for areas well ahead in the direction of the vehicle's movement, and is considered to be of a higher convenience than the former method.
However, even if the map is moved in a scrolling manner, there is a limitation in the extent of the map displayed ahead of the vehicle in the direction of the vehicle's movement because the size of the display area is limited. Furthermore, there will be a user's demand for viewing the map of an area well ahead of the vehicle in the direction of the vehicle's movement.